Several fire departments (brigades) in the UK have been using PPV for the past ten years but it is only recently that it has been approved and adopted as national policy. In the pre-attack mode we have only surmounted a small amount of experience although it has been well researched both here and in Sweden.

I have seen and heard of ignitions occurring in fire gases that have accumulated in the fire compartment itself (I have also seen wind do the same thing). However, it is somewhat concerning that ignitions have occurred on at least two occasions outside the fire room, on stairways leading up to the next level. This is where the fire is in a second storey room and fire travels out and up the stairway towards the third storey.

The PPV airflow travels where there is least resistance and creates a 'venturi' effect - 'pulling' the fire out of the room involved and towards/into the stairshaft.

This has occurred in test burns in real structures.

Bob 1350 - I don't want to create alarm where it is not needed. I am wondering if this is an acceptable risk or if we should avoid PPV in a structure where any airflow in the stairway might 'pull' flaming fire gases to the upper storeys?

I think, in certain types of structure and under certain circumstances PPV is a fantastic tool in pre-attack. I appreciate your caution and hope other firefighters may share any experience they have had so that we can all learn and establish the potential for failure - not to condemn PPV but to optimise our uses of it.

All the best to you both as well and thanks for replying to this post.

I hope this has helped a little.

Keep safe.

I appreciate the points you make and they are acknowledged. However, the situations I talk of all occurred with hoselines charged and correct procedure followed.

There are occasions when fire can be drawn to the unburned area within a structure, depending on the building geometry and path of least resistance - which the fan's airflow will follow. In a stairway there is a phenomena where natural 'stack' effects have 'pulled' fire and heat towards advancing firefighters in past fires - well documented. I would see that this effect could be carried over to situations where the PPV airflow is passing the room/s involved and heading to upper levels, where the path of least resistance exists. As I say, we have noted this effect (in structural test burns) in two different parts of our country.

There are other considerations - if the fire is in a fuel-controlled regime then ignitions of fire gases are unlikely. However, if the fire has become heavily reliant on air supply and is progressing into a ventilation controlled regime, it has been shown that the PPV airflow is most likely to increase the intensity of the fire within the room involved. This is ok for us (firefighters) but is it ok for occupants of the room (who may still be alive)?

I agree Larry, PPV can be the greatest tool - but it has drawbacks, and as users we need to recognise them before evaluating the risk.

I think that PPV will have a 90 percent success rate (ball-park figure)in most situations. Are we in a position to accept the inherent risks? Lets say, if we had a hostage situation with 10 people inside a building - and we 'stormed' the building with our SWAT units with a 90 percent success rate......1 hostage dead but 9 saved....I think that would be a successful operation. What if there were 90 saved but 10 dead?.....not so sure!!

Maybe we should have negotiated a bit longer!!

Stay safe.......

You make a good point about the fire progressing into a ventilation controlled regime, and the fan increasing the intestity of the fire, thus increasing the life hazard for any trapped occupants in the fire room. I have several counter points. First most fire fatalities are due to inhalation of products of combustion, ie smoke, hot gasses, hydrogen cyonide, nitrogen oxide and dioxide etc. The use of PPV can rapidly mitigate this #1 life threat in a fire and increase the chance of survival for any trapped occupants. Second the point of having a charged hose line in place prior to turning in the fan is to make a rapid attack on the fire before the fan can increase the rate of combustion to a dangerous level. Again increasing the chances of survival. Finally because a properly used fan can rapidly ventilate a building, the visibility conditions are much better and the fire fighters have a better chance of finding victims in the building than if they were groping around in the dark waiting for someone to cut the roof. Once again increasing the chance of survival for any trapped occupants.

The key is the PROPER use of the fan. It is a double edged sword that can be a great asset when used properly, and turn around an bite you if you don't know what you are doing with it.

Bob1350 - I agree, where PPV is involved, CAUTION is the safest approach. I guess we could be accused of being over cautious in some respects and this reduces our chances of achieving success - deep respect for those who are willing to experiment! However, lets analyse all the downsides so we can turn them around to our advantage and proceed with 'safe & effective' use of pre-attack PPV.

Larry, I am not sure how much of this data I can supply - these were burns in unoccupied structures by firefighters and I am not certain how specific they were in recording the dimensions etc. However, they were pretty specific on how the gases ignited above their heads in the stairshafts!!! I will find out what I can.

I have just got hold of an interesting scientific test document that reports on over 40 test burns (in UK) where the effects of PPV air-flows were analysed in the stairshaft of a multi storey building with a fire in a second storey room. The document is pretty extensive and I am away for two weeks. I will publish a brief summary of this report!in this post around 5-6th August as its pretty relevant to the discussion.

The report!concluded that the use of a PPV fan can improve conditions in a smoke logged stairwell, improving overall visibility to some extent while having no adverse effect upon the temperatures in the stairwell. However, the report!also stated that stairwell and compartmental (fire room) temperatures were seen to rise (peak) under certain circumstances and that whilst PPV will usually improve conditions in a stairwell it is virtually impossible to predict exactly what the effect of a fan will be in a given situation with any degree of certainty.

If the aim is to pressurise the stairwell to prevent egress of contaminants from the fire floor it was suggested that all vents in the stairwell should remain closed and a 'small' outlet point should exist/be created in/near the fire compartment. The report!went on to state that a 'large' outlet may result in a negative pressure in the stairwell with 'the possibility of smoke (and gases) leaking into it'.

Unfortunately the fire sources were 20 and 40 liters of Heptane in trays and were not effectively reproducing 'common' fire gases in the stairwell.

The report!confirms that it is possible for a PPV airflow to create a negative pressure in a stairshaft that may serve to 'draw' fire gases (and fire) towards the stairwell. Although this effect is unlikely it is possible and is subject to varying conditions and airflow paths that may not be obvious at the outset of operations.

The use of PPV in a multi storey building can have both good and bad results. It is easy to state 'text book' guidelines (as Lt706 does) but in reality, there are too many variables at the outset of most operations that cannot be known for some time, possibly even until the fire has been extinguished.

I am fully in support!of using PPV in 'attack' situations but consider that in certain situations we are going to 'worsen' conditions. However, I do realise that lives ARE going to be saved and firefighting IS going to become generally easier and SAFER by using PPV in pre-attack mode. We just need to be aware of the risks, share our experiences and train our firefighters to ensure we maximise this valuable fire attack tool.

PPV with Training.....PPV with Caution!

and keep safe.............

The big thing in my department is this.

We have over 90 firefighters, all of which are volunteer, and a career chief. The chief is totally against PPV, but in my mind, PPV is just like anything else. You need practice, training, etc. I am not knocking him, and I have printed some of your posts, as to try and benifet the department. Any thoughts or input?

We do use PPV to find hot spots, etc, but well after the fire is under control. I would much rather get the training needed, as to help me see better, prevent flashover/backdraft, and help protect not only myself, but everyone involved.

Thanks

Take Care and Be Safe